Leaning on Climb Out

3Y3Flyer

3Y3Flyer

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3Y3Flyer
I fly a PA28 180, and the POH is not all that great when it comes to leaning. Full rich below 5000' then basically as required. I am an Iowa flat lander, so for the most part DA is not a huge issue unless we have a really hot day. SOP is lean for taxi, full rich for TO, lean as required above 5000', ROP for cruise.

I recently flew to AMA and took notice of the higher DA and leaned for best performance on TO...then continued to lean through the climb to cruise, balancing EGT, RPM, and CHT temps. Always sacrificing climb to maintain a CHT at or below 400 on my hottest cylinder. Performance was outstanding, especially climbing past 070 through 110, and I have since been doing that on every flight.

My question is this....from a mechanical stand point, is this practice harming the powerplant in any way? As I said the POH is crap for information on this, and I don't need to be buying a new engine any earlier than TBO.
 
You should not lean when power is higher than 75%. Takeoff from sea level will produce 100% power, so that is why you need full rich on takeoff. At high density altitudes you can lean even during takeoff. Once you have reduced power to below 75%, you can lean as much as you want. That could be due to throttling back or from climbing to a higher altitude.
 
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75% is what I grew up with. Anything above 5,000ft, since theoretically my normally aspirated O360 can’t make more than 75%, too.

Back to the OP, my understanding is what you’re doing is fine but I’m some anonymous non-A&P on the internet. The book says to lean to max RPM then put a bit back in for takeoff at high DA fields. On climb, above 5000 I lean to max RPM and keep tabs on the CHTs. As long as they’re below 400 I’m happy (I’ll even tolerate a few degrees more).
 
I’m far from an expert on the subject. My thoughts are that the POH was developed long before engines had EGT/CHT for each cylinder. If at sea level your full power/rich mixture results in an average EGT (call it 1380) then as I climb I keep pulling the red levers to maintain close to the average while maintaining CHTs under 400.

I feel like the old 5000 ft rule was just to overly simplify things based on equipment and training/knowledge at the time. Don’t think that’s the most efficient way to operate.

*I reiterate, far from an expert.*
 
Llewtrah381 said:
75% is what I grew up with. Anything above 5,000ft, since theoretically my normally aspirated O360 can’t make more than 75%, too.
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Rule of thumb for power loss at altitude is 3% per 1000ft. 5000ft would give a max available of around 85%.

If you are willing to go through the chart, you can figure out the exact amount:
https://www.lycoming.com/sites/default/files/O-HO-IO-HIO-AIO & TIO-360 Oper Manual 60297-12.pdf
upload_2021-6-2_18-5-49-png.96907
 
Thanks guys, that helps clear it it up a bit in my head. So basically any climb at full rich looses power as you climb, by leaning in the climb and or at TO in higher DA, you try to obtain the 75% power rating for xyz altitude. KISS principle...keep the CHT below 400 and the RPM's @ 75% via altitude.
 
asicer said:
Rule of thumb for power loss at altitude is 3% per 1000ft. 5000ft would give a max available of around 85%.

If you are willing to go through the chart, you can figure out the exact amount:
https://www.lycoming.com/sites/default/files/O-HO-IO-HIO-AIO & TIO-360 Oper Manual 60297-12.pdf
upload_2021-6-2_18-5-49-png.96907
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My bad.

3Y3Flyer: your engine’s gonna blow up

Seriously, I have %HP on my EDM 830 and lean when it’s less than 70%, just to make sure if I mis-calibrated the HP constant I’m still OK. That said, I had understood the 75% was even a conservative figure for preventing detonation.

This is why I qualify my posts with reminding people I’m a non-A&P stranger on the internet.

BTW: the chart above looks different than what’s in my POH but point taken.
 
I remember my POH says you can lean at 75%, which equates to 2500 RPM at 2500'. It goes up about 25 RPM per thousand from there.
 
Then there’s this my POH (Archer II but I actually have a Warrior with the Archer’s engine):

7F863AB7-81D1-4956-A258-E709C1232146.jpeg
 
Dan Thomas said:
Lycoming recently (and quietly) changed their recommendation from below 75% to, I think, 65%.

Whatever the POH says. If it doesn't have much detail, look for the Lycoming O-360 Operator's manual and go through it.

Did it for you:

View attachment 97138

From https://www.lycoming.com/sites/default/files/O-HO-IO-HIO-AIO & TIO-360 Oper Manual 60297-12.pdf

Page 3-6.
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Curious about the difference in allowable CHT between high performance and economy cruise. Is the rationale that the mixture will be richer for hp cruise and therefore less prone to detonation? HP cruise would seem to be more abusive to the engine than economy cruise so why the higher allowable CHT?
 
To the OP - my pa28/180 is based in Las Vegas. At this time of year DA at takeoff is around 5000. I lean for best power, and then every 1000' (ish) in the climb continue to lean trying to ensure CHT stays below 400 even if it means sacrificing climb rate.
 
One way to do it is to note your EGT temp at takeoff, then lean to maintain that EGT through out the climb until you lean for cruise or for operations under 65% power.

Brian
 
Alien Mind said:
To the OP - my pa28/180 is based in Las Vegas. At this time of year DA at takeoff is around 5000. I lean for best power, and then every 1000' (ish) in the climb continue to lean trying to ensure CHT stays below 400 even if it means sacrificing climb rate.
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If leaning is reducing cylinder head temps you are operating LOP. LOP operations are not generally recommended in climb or at high power settings.
 
It’s been a while since I immersed myself in this stuff, but here’s where I got the 60% figure for the highest percentage of power where you’re 100% safe to lean however you like:

51238924135_874af97ec8.jpg


It’s call the “Red Fin” and was proposed by Mike Busch of Savvy Aviation. The idea is cylinder pressures in that red area are higher than desired and therefore best avoided for engine longevity. Clearly, the higher the power the wider the fin. But pull back to 60% - or climb to an altitude where that’s the most your NA engine can produce - it’s gone completely.

That’s a very quick summary of the concept. It’s easy to find lengthy articles by him in Pelican’s Perch and elsewhere. Worth the time and effort.
 
brcase said:
One way to do it is to note your EGT temp at takeoff, then lean to maintain that EGT through out the climb until you lean for cruise or for operations under 65% power.

Brian
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Nailed it. Easy peasy.
 
Jeff767 said:
If leaning is reducing cylinder head temps you are operating LOP. LOP operations are not generally recommended in climb or at high power settings.
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Best to say only go LOP in the climb or at high power if your’re committed to going LOP enough. I believe LOP climb is SOP in the turbocharged Cirrus.
 
Dan Thomas said:
Lycoming recently (and quietly) changed their recommendation from below 75% to, I think, 65%.
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What is the reason for full rich above 75%? I know pilots who lean for max power on take off. Frequently that is full, but on higher DA days it isn't.
 
bflynn said:
What is the reason for full rich above 75%? I know pilots who lean for max power on take off. Frequently that is full, but on higher DA days it isn't.
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The excess fuel is needed for cooling.
 
sarangan said:
The excess fuel is needed for cooling.
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Sure, running richer runs cooler.

So the recommendation is a proxy for engine temperature and if you have other ways to monitor temps, then you're safe to run leaner for power?
 
bflynn said:
Sure, running richer runs cooler.

So the recommendation is a proxy for engine temperature and if you have other ways to monitor temps, then you're safe to run leaner for power?
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Air flow and excess fuel provide cooling. If you have high power and low air flow (such as during a climb) then you need the excess fuel for cooling. If you have moderate power and high air flow, then you can lean the fuel flow. If you have low power, you can lean regardless of air flow. In other words:

100%-85% power: Mixture should be rich always
85%-75% power: You can lean if you have adequate air flow. This means you should be in cruise configuration with the cowl flaps open.
Below 75% power: You can lean regardless of air flow.

The 5000 ft number that is often mentioned in POH corresponds to the 85% power if you are at full throttle.

I am sure someone will correct me if I am wrong.
 
sarangan said:
Air flow and excess fuel provide cooling. If you have high power and low air flow (such as during a climb) then you need the excess fuel for cooling.
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This is not necessarily true. Yes, in a high power Vy climb, you'll have less airflow. In a cruise climb you have more and can easily keep CHTs down.

If "lean below 5000" is all about cylinder temps, then that's the understanding I needed. My checklist says to lean for cruise with no regard to altitude. For a short hop, cruise might be 3000', but temps are well below 400. Ok, the engine isn't going to explode on me ;)
 
bflynn said:
This is not necessarily true. Yes, in a high power Vy climb, you'll have less airflow. In a cruise climb you have more and can easily keep CHTs down.

If "lean below 5000" is all about cylinder temps, then that's the understanding I needed. My checklist says to lean for cruise with no regard to altitude. For a short hop, cruise might be 3000', but temps are well below 400. Ok, the engine isn't going to explode on me ;)
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Yes, CHT is the critical value to monitor. But that assumes you have a well behaved CHT probe. In our club plane, the CHT is very flaky, so I rely on power setting. Here is a good article by Mike Busch that is worth reading. https://resources.savvyaviation.com/understanding-cht-and-egt-2/
 
6 cylinder analyzer. I start leaning right away and keep the CHTs below 375. These POHs were written before multichannel engine analyzers were around, or assume you don't have one, or just write it for the least common denominator.

I suppose bloodletting is still a viable medical practice for every ailment, too?
 
Some non- A&P thoughts here:

Seems to me we’re dealing with two different but related engine phenomena here. The first, and what seems to be most talked about here in the past few posts, is CHT, which I’d contend is a long-term engine health issue.

More important, and an immediate risk to engine survival, is detonation. THAT is the part I’ve always understood the 75% to relate to. Below 75% HP, by my understanding, and the risk is sufficiently low for detonation that one can lean as aggressively as they want without risk of detonation - but CHT could still be high. My understanding is you can most definitely get detonation even with a comfortably low CHT, so that’s not a realistic measure for detonation risk.

I may be way off here but I suspect the POH language I cited above deals with detonation risk and not CHT: IN CRUISE FLIGHT (i.e. level) above 5,000 the pressures in the cylinder are not able to get high enough to cause detonation if spinning an appropriate propeller, etc. I know in my plane I can still easily exceed 400 CHT in cruise at 5,000 - even higher - even with not-terribly-aggressive leaning. But I’m led to believe detonation risk is low despite the CHT.

But the point here is detonation is the much more imminent risk, not CHT.
 
Llewtrah381 said:
But the point here is detonation is the much more imminent risk, not CHT.
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You have it right. Anything that slows the combustion gives time that allows the complex fuel molecules to break down into simpler, easily-autoignitable molecules, and we get detonation. Flame front that travels at 5000 feet per second instead of 100 FPS. It takes the engine apart. Big cylinders take longer to burn. Low RPM gives more time. Aircraft engines have both of those. Lean mixtures burn more slowly. Hotter induction temps and/or higher compression raise the charge temperature so that the molecular breakdown happens sooner. Rich mixtures cool the air charge and cool the combustion process and the cylinder/head itself.
 
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This has been a very informative thread. Several misconceptions demystified with respect to CHT, detonation and power limits for leaning.
 
Continental's rules say you can do whatever you like with the mixture as long as you're below the max continuous power rating.
 
3Y3Flyer said:
Full rich below 5000' then basically as required.
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Do you mean this to say that you're flying along in cruise below 5000, full rich? If so, that's needlessly wasting fuel. You should always lean as appropriate in all phases of flight.

And of course, it's also significantly shortening your range. In fact, I know someone who ended up in a major accident, totaling the aircraft and causing long term health effects, who ran out of fuel after something like only 3.5-4 hours in an Archer. Now, an Archer can easily fly for 5 hours with full tanks, which this plane had on takeoff. The hypothesis was that he didn't lean, ended up running out of fuel, and crashed in the trees.

On another note, the 5000 feet that Lycoming states in their manual for the O-360 as "full rich will cause rough running" really is pretty accurate. I teach a lot in a Seminole, with carbureted O-360s, and on climbout passing about 4500 at full throttle (around 24" at that altitude, and props pulled back to 2500 as specified in the POH), it will very reliably start running rough with the mixtures at full rich. Lean it out some, and it smooths right out.
 
Back when I taught for Burnside-Ott at Opa Locka in the 1970’s, we taught leaning even to and from the practice area. Law of Primacy and all that. Saved a lot of gas for the school and better on the engines as far as lead accumulation. Second step for maneuvers was “2. MIXTURE RICH” (Step 1 was clearing turns). But it was not at all rare to pick up students from elsewhere who essentially had no idea when and how to use the mixture control.
 
Was there a time 3000 feet was the magic number for verboten leaning? That's what I remember, and I have pretty much stuck to it except in climb (enriched) and taxi (way leaned). I generally poke along at 65-70% power as I'm never in a rush to get anywhere and in cruise I lean regardless of my altitude--lean to stumble, enrichen to smoothness. Yes, it's old school.
 
FastEddieB said:
Back when I taught for Burnside-Ott at Opa Locka in the 1970’s, we taught leaning even to and from the practice area. Law of Primacy and all that. Saved a lot of gas for the school and better on the engines as far as lead accumulation. Second step for maneuvers was “2. MIXTURE RICH” (Step 1 was clearing turns). But it was not at all rare to pick up students from elsewhere who essentially had no idea when and how to use the mixture control.
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I have a question: I’ve seen many maneuver documents that are similar in “Full Rich” before beginning maneuver. I’ve seen even more pilots doing it.

Example, on a flight review or checkride prep: “Let’s see you do slow flight”. Student says, “ok” and proceeds to go Full Rich at 3,500 feet, then pull the power back to probably 45% to start slowing down.

Good lord, WHY? Steep turns? Probably done at 60-65% power to get down to Va. Full rich they go. WHY?

I’m pretty sure the answer is that no one taught all these pilots what the red money knob does.

Makes my wallet hurt.


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Domenick said:
Was there a time 3000 feet was the magic number for verboten leaning?
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believe thats the Cezzna school of thought - seriously, all POH in the flight school i did my primary in 172 had 3000, then i got into archer and the magic number is 5k. whatever.

i normally drone around at 60% or even less if i am just out and about and pull the red knoc way back burning like 6.2 gal/hr. if i am going somewhere, 65%, leaned, you cant hurt anything with that. whatever TAS i get is fine. I didnt buy the archer to go somewhere fast lol

Edit: if you have an engine monitor, it gets even easier. lean to your best power, as you barrel down the runway (take DA into consideration), note the EGT numbers right at take off and as you climb, keep leaning to get as close to that number as you can with WOT
 
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crash7 said:
I have a question: I’ve seen many maneuver documents that are similar in “Full Rich” before beginning maneuver. I’ve seen even more pilots doing it.
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I was taught the same way. fuel pump on, mixture full rich. Fuel pump on i get, mixture not so much
 
WannFly said:
I was taught the same way. fuel pump on, mixture full rich. Fuel pump on i get, mixture not so much
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I think the correct answer is “it depends”. Power on stalls is a good example. Full rich? Well... to simulate a botched takeoff, we should configure the plane like we’re taking off. Here in the flat lands that is indeed full rich.

If we’re demoing this maneuver at 3,500 however, then we’re right back into the discussion of the thread. Full rich? Probably not. Leave it leaned at cruise at 3,500? Probably not. Somewhere in between? Yup.


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